1. Field of the Invention
The present invention relates to a long glass fiber filler reinforced resin material for molding, in which a composite of a matrix resin including a polypropylene (hereinafter, referred to as “PP”) component and a long glass fiber filler is formed as a masterbatch and the masterbatch is diluted with a diluent resin made from an ethylene-propylene block copolymer, a method for molding a molded article and a molded article molded by the method.
2. Discription of the Prior Art
Long glass fiber reinforced resin materials comprising a composite of about 10 mm length of a long glass fiber filler and a resin are widely used as materials for various industrial articles such as automobile parts, because of their excellent mechanical characteristics and molding processability.
As an example of such resin materials, JP 7-232324 A discloses a material obtained by the following method. A denatured PP resin having a melt flow rate (hereinafter, referred to as “MFR”) of 70 to 300 g/10 min is melted, and glass fiber bundles are impregnated with the melted denatured PP resin. Thereafter, the resultant is cut to a length of 2 to 50 mm into pellets, which are masterbatch, and the masterbatch is diluted with a PP resin. This constitution is directed to improving the dispersibility of the long glass fiber filler in the masterbatch produced by a drawing method, and preventing deterioration of the strength of a molded article due to dilution of the masterbatch with a PP resin.
JP 3-25340 B discloses a blend of a long glass fiber filler reinforced pellet comprising low molecular weight thermoplastic polymer and at least 30 volume percent of glass filaments for reinforcement, and thermoplastic polymer having a higher molecular weight than that of the thermoplastic polymer contained in the pellet. This constitution is directed to improving the wettability of the resin with respect to the long glass fiber filler and improving the bending modulus of a molded article.
JP 11-152062 A discloses a front end for automobiles produced by injection-molding a raw material comprising thermoplastic resin pellets containing 20 to 80 mm mass percent of glass fibers of a full length of 2 to 100 mm arranged in parallel to each other, using a thermoplastic resin (PP, ethylene-propylene block copolymer, etc.) as the matrix. The content of the glass fibers of the front end is 15 to 50 mass percent, and the weight average fiber length is 1 to 20 mm. This publication describes that this constitution can ensure excellent vibration fatigue resistance and impact resistance and can suppress warping.
JP 2721702 B discloses a composition obtained by blending propylene polymer (propylene homopolymer or the like) and a reinforcing material (glass fibers or the like). The propylene polymer has a MFR of about 55 to 430 g/10 min, and the reinforcing material is contained in a ratio of about 20 to 65% based on the total mass of the propylene polymer and the reinforcing material. This publication describes that with this constitution, the flowing characteristics are better than those of a fiber reinforced composition made of a polymer with a low MFR, and at the same time, deterioration of the characteristics of the composition regarding the strength and the rigidity of a molded article can be prevented.
JP 6-340784 A discloses a propylene based heat resistant resin molding material comprising 3 to 97 mass % of a glass fiber bundle structure and 97 to 3% of a crystalline propylene based polymer (propylene homopolymer, ethylene-propylene copolymer, etc.) having a MFR of 50 g/10 min or more. The glass fiber bundle structure comprises 20 to 80 parts by mass of glass fibers for reinforcement substantially all of which have a length of at least 3 mm and a diameter of 20 μm or less, and 80 to 20 parts by mass of a crystalline propylene based polymer (propylene homopolymer, ethylene-propylene copolymer, etc.) that is at least partially denatured with unsaturated carboxylic acid or the derivatives thereof and has a MFR of 50 g/10 min or more in the entire polymer. In the glass fiber bundle structure, the grass fibers for reinforcement are arranged substantially in parallel to each other in the polymer component. This publication describes that with this constitution, a molded article obtained by injection molding or the like has excellent heat resistance, moldability, and anti-warping properties, and a small weight, so that the molded article can be applied to automobile parts that should have a small weight, and requires high heat resistance and molding dimensional stability. This publication also describes that the impact strength and the anti-warping properties of the molded article can be improved by adding at least one elastomer selected from ethylene based elastomers (ethylene-propylene copolymer rubber (EPM), ethylene-propylene-nonconjugated diene terpolymer rubber (EPDM), etc.) and styrene based elastomers (hydrogenated styrene-butadiene block copolymer, etc.).
JP 11-228759 A describes a propylene based resin composition comprising 90 to 30 mass percent of a propylene based resin (propylene homopolymer, ethylene-propylene block copolymer, etc.) having a MFR of 1 to 1000/10 min., a pentad isotactic index of 95% or more in the propylene homopolymer portion, and an elusion amount of 2.0 mass percent or less at 40° C. or less by chromatograph, 10 to 70 mass percent of elastomer (ethylene-propylene copolymer rubber (EPR), ethylene-propylene-diene copolymer rubber (EPDM), etc.) having a MFR of 0.1 to 100/10 min, and an inorganic filler (glass fiber or the like) in a ratio of 5 to 75 mass percent based on the total mass of the propylene based resin and the elastomer. The publication describes that with this constitution, a molded article molded by injection molding is significantly improved in the scratch resistance and the bending modulus.
WO01/72511 describes a long glass fiber filler reinforced resin material for molding comprising a matrix polymer, a long glass fiber filler and an affinity providing component for providing affinity between them, wherein at least the matrix polymer and the long glass fiber filler constitutes a composite. Herein, the matrix polymer includes a PP component having a pentad isotactic index of at least 95%, a MFR of the matrix polymer is 100 to 300 g/10 min, and the long glass fiber filler is in a content of 30 to 50 mass percent with respect to a total mass. The publication describes that with this constitution, since the MFR of the matrix polymer is at a high level properly (the molecular weight is small), breakage of the long glass fiber filler can be prevented effectively, so that a molded article having a high impact strength can be obtained. Further, it describes a long glass fiber filler reinforced resin material for molding comprising a masterbatch and a diluting polymer. Herein, the masterbatch comprises a matrix polymer including a PP component having a pentad isotactic index of at least 95%, a long glass fiber filler and an affinity providing component for providing affinity between them, wherein at least the matrix polymer and the long glass fiber filler constitutes a composite and the diluting polymer includes a PP component having a pentad isotactic index of at least 95%. Further, a MFR of the matrix polymer of the masterbatch is larger than twice a MFR of the diluting polymer, and the long glass fiber filler is in a content of 30 to 50 mass percent with respect to a total mass. The publication describes that with this constitution, the matrix polymer of the masterbatch and the diluting polymer have a large difference in the viscosity between them, and also the former has higher wettability for the long glass fiber filler than that of the latter because the former has lower viscosity than that of the latter, so that a state where the long glass fiber filler is covered with the matrix polymer can be maintained. As a result, breakage of the long glass fiber filler can be prevented effectively and a molded article having high impact strength can be obtained.
Examples of a method for molding a resin into a molded article include press forming and injection molding. When the two methods are compared, it is difficult to mold a complicated shape by press molding, whereas it is easy to mold a complicated shape by injection molding and therefore the degree of freedom of molding is high in injection molding. Further, press forming requires post-processing such as stamping for openings or the like, whereas injection molding does not require such post-processing, and therefore the processability is good in injection molding. Further, press forming requires the process of setting a resin plate (blank) to a mold, heating, and compression, whereas only injection of a molten resin into a mold is required and continuous molding can be performed in injection molding, and therefore the productivity is high in injection molding. Therefore, in view of the above points, injection molding is better than press forming.
However, when the same long glass fiber filler reinforced resin material is used for molding, the article molded by injection molding and the article molded by press forming have the same level of bending strength. However, the former has significantly lower impact strength (Izod impact value) than that of the latter. It is known that the bending strength of the molded article depends on the amount of the contained long glass fiber filler, whereas the impact strength depends on the fiber length of the contained long glass fiber filler. Accordingly, the above-described phenomenon implies that the long glass fiber filler is broken and made short in the process from the introduction of a material to the end of molding in injection molding. In fact, according to the experiment results, in press forming, when a resin material comprising a long glass fiber filler having a fiber length of a little more than 10 mm is used for molding, the length of a long glass fiber filler extracted from the molded article is about 10 mm. On the other hand, in injection molding, when the same resin material is used for molding, the length of long glass fiber filler extracted from the molded article is about 0.9 mm. As shown in FIG. 9, the long glass fiber filler 9 seems to be broken in the following manner. A solid phase 7 and a melting phase 8 of a resin are formed in a cylinder of an injection molding machine, and the long glass fiber filler 9 is bended by shearing between the resin phases at the interface between the solid phase 7 and the melting phase 8, and thus is broken. Alternatively, the long glass fiber filler 9 seems to be broken because the long glass fiber filler 9 is bended by buckling during shear flow of the resin in the melting phase 8.
The above-described problems have been tackled by improving the dispersibility and the adhesive properties of the long glass fiber filler as described in JP 7-232324 A to improve the impact strength. However, this level is not yet comparable to that of the article formed by press forming. The impact strength can be improved further by adding PP elastomer or polyethylene elastomer. However, such an approach deteriorates the bending strength.
Further, when a molded article having thin portions with a thickness of some mm is molded by injection molding or injection compression injection, it is necessary to increase a clamping force of the mold so that a pressure in mold can be higher than usual in order that the melted resin material is filled within an entire mold cavity of a mold for molding. However, such forming the molded article by increasing the pressure in mold under high clamping force may cause a problem that internal strain occurs easily in the formed molded article and deformation such as warping occurs during its releasing. Further, the following problem may exist. That is, since clamping force of the mold that is allotted to each molded article for molding is made high, the number of the molded article that can be obtained by one supply of the melted resin material decreases. As result, the productivity of the molded article may be low.